Problem: $\dfrac{7}{10} - \dfrac{7}{6} = {?}$
Explanation: $ = {\dfrac{7 \times 3}{10 \times 3}} - {\dfrac{7 \times 5}{6 \times 5}} $ $ = {\dfrac{21}{30}} - {\dfrac{35}{30}} $ $ = \dfrac{{21} - {35}}{30} $ $ = -\dfrac{14}{30}$